18 Gr. O. Sars. 



occurring in the larva being replaced by a very small denti- 

 form projection. 



The branchial legs are now so fully developed, as to 

 admit of being moved in the rhythmical manner character- 

 istic of the adult animal. Behind the 6 pairs already found 

 in the last larval stage, 2 additional pairs have developed, 

 the total number of legs being accordingly 8 pairs. 



The pedigerous part of the trunk in this stage shows 

 the first trace of segmentation, and from the segments the 

 dorsal, hairy protuberances are seen growing forth, their 

 number being, in this stage, only 4. 



The caudal part, or tail, is still but little deflexed, and 

 thereby less conspicuously marked off from the adjoining 

 part of the trunk. It is, however, constructed in essentially 

 the same manner as in the adult animal, the caudal claws 

 being now well defined and movably articulated to the an- 

 terior corner. Each of the caudal plates is produced at the 

 lower corner to a strong spiniform projection, and between 

 this projection and the knobs carrying the caudal setæ, only 

 a single denticle is as yet developed on each plate. Just 

 above the caudal setæ, as in the adult animal, a pair of 

 dentiform projections occur, and in front of them there are 

 traces of another pair. 



Of the inner organs, the alimentary tube is very con- 

 spicuous by its yellow contents which turn to dark brown in its 

 posterior part. Anteriorly, it has on each side a well-defined 

 cæcal appendage, which is slightly bilobed and forms the 

 commencement of the liver. The heart is also distinctly 

 observable within the anterior part of the trunk dorsally. It 

 is rather elongated, and exhibits on each side 4 venous 

 fissures. 



The body is still highly transparent and almost colour- 



